Codon usage: the effective number of codons (Nc) used within the longest MPV gene (L). Sequences included as in Table 1.

<p>The curve represents expected codon usage in relationship to the GC3 content, therefore at 50% GC content all synonymous codons should be used equally in the absence of other factors. Nc values range from 20 when only one of the possible synonymous codons is used for each amino acid, to 61 when all synonymous codons are used. The closer the Nc value is to 20, the stronger the codon usage bias is, and the higher the degree to which codons are used non-randomly. HMPVs (Nc = 41.9 to 43.2) AMPV-Cs (Nc = 47.1 to 47.5) and AMPV-A, B, D (Nc = 51.4 to 52.7).